Pretty much what SnowpointQuincy said. Its no easy feat to get the Shiny Charm. Nor is it easy to get the two in game Shiny Pokemon. Banjiro is fairly hard to get to unless you are familiar enough with how to battle in these kinda battles (Battle Tower and the like) Most recreational players probably wouldn't get that far into it just for a Shiny Dragon at level 1.

Haxorus can't be visited until you get to a certain Pokedex achievement which is still difficult to do unless you are really good at trading or own two different copies and have a lot of time on your hands.

Even with the Charm's effect, its still plenty hard to get a Shiny Pokemon. I've bred tens of thousands of eggs with a Japanese Ditto in Pearl all the way to Black and never have gotten a Shiny through it. I caught 1 Shiny in every generation that Shinys were available.
Drowzee in Gen 2
Wurmple in Gen 3
Shinx in Gen 4
Tympole in Gen 5

The last happened a few weeks ago. I breed about 10 - 15 eggs a day for personal use and sometimes to shiny hunt. While the Charm makes it a bit easier, I'm still not guaranteed a shiny encounter easily, I still have to work to get them.